Prominent amnion-chorion separation between 13 and 15 weeks gestation is associated with increased risk for fetal chromosome abnormalities

Abstract

The past decade has witnessed the expansion of ultrasound technology into prenatal genetic screening with the application of ultrasound for fetal aneuploidy risk assessment using nuchal translucency measurement. It is well accepted that prominent separation of the amnion and chorion membranes is a commonly observed finding in first trimester pregnancies. However, recent work and experience have suggested that such separation may be associated with an increased risk of chromosome abnormality when found in the late first and second trimesters. We thus evaluated our most recent (1997 – 1999) prenatal diagnostic cases from 13.0 to 14.9 weeks' gestation, inclusive. Of the 247 cases, 14 cases (5.7%) were characterized by an amnion-chorion separation (at any given point and not necessarily uniform) of 15 mm or greater. The measurement of amnion-chorion separation was achieved by averaging 3 separate views of the membranes Of these 14 pregnancies, 6 (42.9%) were characterized by abnormal fetal complements: 3 cases of trisomy 21, 2 cases of trisomy 18 and a single case of 45,X. Of note is that all but 2 of the cases of trisomy 21 demonstrated concomitant ultrasound-detected fetal structural' defects at the time of ultrasound examination.

Conclusions: Our findings from this preliminary study demonstrate that prominent amnion-chorion separation at or after the 13^th gestational week may be associated with an increased risk for fetal chromosome abnormalities. Further work is needed to determine whether this is an independent marker for fetal chromosome abnormalities and whether such findings are reproducible at other centers.